I'm about to order my radiators for the van, (Ultraheat do down to 200mm
wide rads, just waiting for a price) still waiting for the boiler
(eberspacher diesel fueled hot water furnace) to arrive, so whilst i'm
waiting i'm going to run the pipes for the radiators.

Never done any central heating work before, so any tips welcome, tho i
imagine half the things applicable to a house arent to a van... or maybe
they are.

The system is basicaly going to be a single boiler and 2 pumps, one for the
calorifier (small hot water cylinder) that part is easy, from the outlet of
the boiler a pipe goes to a Y piece, then to the 2 pumps, pump one then has
a pipe from the outlet of the pump to the calorifiers coil inlet, the outlet
goes to a Y piece and back to the boiler return, that circuit compleated,
simple etc.

For the central heating, i run a pipe from the outlet of pump two, around
the van, and back to the Y piece to the boiler return.

The boiler will be situated about halfway down the van's length, on the
right hand side in an underfloor locker, a 15mm pex (speedfit) pipe will
come off the pump and go through the floor into the living area, it'll loop
backwards slightly and then go down to the back end of the van about 4
meters, then turn right accross the van for 2 meters, then turn again to
come up the left hand side of the van, it'll go up for 4 meters and that's
the end of the flow pipe, it then loops around and follows the pipe back to
the boiler.

The radiators, one will be off the begining of the pipe where it loops back
slightly when it enters the living area from the floor,

the second rad will be at the back of the van, on the left hand side just
after the pipe turns the corner,

And the last rad will be at the end of the pipe run where it loops back,

i'm using thermostatic valves on all rads,

problem i see is, how on earth do i stop the first radiator with a full open
flow valve allowing all the hot water to go through the rad and into the
return line, thus avoiding the water going round the rest of the pipework?

And more importiantly, how do i stop the last rad on the pipes being
bypassed because that's where the flow becomes the return line??

I dont really want to have a rad with no thermostatic valve on it as used in
home heating sytems, and eberspacher recomends that you just put thermo
valves on all rads, and the boiler takes care of it's temperature to when to
shut off and start up... when the water temp is at something like 86 degrees
for 5 minutes it shuts down but keeps the pump running, when it drops to
about 79 it starts up again, so no need for a room stat on this system.

Do i have the last radiator piped up as the return junction... i.e. flow
goes into the rad, return comes from the rad rather than Teeing off the flow
and return pipes as the other rads do?
then fit one of those differential bypass valves near the pump? this thing
flows 900 litres an hour, not sure if that's low or high compared to home
systems.

or would i put the bypass valve at the last rad connection?? or do it a
totaly different way altogether?